The present invention relates to a decompression device comprising a control shaft, an internal combustion engine which has a camshaft with at least one cam having a base circle and a lobe elevated therefrom, a valve acting in association with a combustion chamber, and a transmitting member, e.g., a push rod, transmitting the lift of the cam to the valve, and more particularly to a decompression device used in such an engine, the decompression cam and a ratchet wheel connected to the control shaft, and a shifting member interacting with the ratchet wheel for resetting the decompression cam.